HEF many write cycles

[Ttelmah]

One comment though. You seem to just be talking about storing something
like a 'count' of how many times the signal goes off/on, or just that it is
actually off/on. Both seem rather pointless. Unless you know 'when' the
signal changes, knowing how many times it has changed can be done far
easier with simple mechanical counter. Knowing that it is off or on, well
again the light itself says this. This is why I expected you would really need
something like 'when' it had changed to actually say anything useful. If this
is only a low frequency signal, one way that this could easily be done, is just
to keep the PIC powered. I have remote control units using small PIC's
like this that run for several years on a simple button cell, at a low speed
like 32KHz. If you don't need anything 'quick', this is a much easier solution
than trying to use the HEF.....

[temtronic]

hmm, I'm thinking he wants to 'restore' the light based on what it was before the PIC power was lost. if the light was on, then turn the light on when PIC program runs again. If off before ,then leave light off
So a 'restore to previous condition' flag, not an actual counter of 'on-offs'.

There's a huge problem with the English language, so many ways to describe what you want but then even more ways to interpret what is written....At 68 I'm still trying to figure it out....

[rodrigo_cirilo]

[rodrigo_cirilo]

a doubt, when I connect the pic to pickit3, it shows me pic 10F322, which is powered from 2.3 to 5.5V, if this pic were the 10(L)F322 which is powered from 1.8v to 3.6v the pickit3 would show the letter (L) ?

[Ttelmah]

Try reading the device ID byte, and see if the ID is for a 10F or a 10LF.
It is possible that the PK3, just reports 10Fxxx, for both chips.
The device ID's are in the 'programming specifications' data sheet for the
chips. Should be 0xAC for the 322, and 0xAE for the L version.

Now on this 'restore last state' program, what puzzles me with this is if
the chip is driving the light based on an external signal, then even if you
store the 'last' state, this will be overridden by the current state of the
signal?.
Seems to imply that the control must be coming from something other
than a simple input. Possibly a remote control signal or something
similar?.
In all cases there is a very large problem, unless you can detect that
a power fail is happening. The reason is that if a write to the flash memory
is occurring when the power fails, this can result in complete corruption of
the flash memory. So using the HEF, could be a 'disaster waiting to
happen', unless you can add circuitry to detect that the power is failing.
This is a caveat with all writes like this. The same is true (but less
disastrously), to writes to EEPROM. 'Less disastrously', since corruption
of this does not corrupt the actual program code, but it still results in
corruption of the memory sometimes. If you can arrange to detect that
a power failure is happening, then this makes the 'only write when the
power goes off' solution a much better was to go.
I think you are probably going to have to rethink your hardware a little
to have any hope of making this actually work reliably.

[rodrigo_cirilo]

[Ttelmah]

Though a lot better, it still involves a slow write. On the EEPROM, if a
write gets interrupted, only one byte would be damaged. However I still have
to just recommend a clock chip. Uses the same number of wires as the
EEPROM, and gives you RAM, that writes instantly (nSec).
If you are adding parts, then there are 8pin PIC's that have the EEPROM built
in, instead of HEF, or offer a power fail interrupt (or a comparator that can
give this).

[rodrigo_cirilo]

[temtronic]

I just checked www.banggood.com and they have DS1307/AT24C32 modules for $3 each( $9 for 3 pcs), and DS3231/AT24C32 for $12 for 3 pcs, CDN money.
The DS3231 is a far more accurate RTC, but only 7 bytes of battery backed RAM, the DS1307(older RTC..) has more BB RAM but less accurate clock.

While I don't have a problem getting PICs, I decided years ago to buy ONE big PIC, the PIC18F46K22 , and use for ALL my projects. It has 40 pins, lots of memories, 2HW UARTS, etc. Far more 'stuff' than needed, BUT, it has allowed me to create my own libraries of working functions and almost 'know' the PIC. There's also the baby sister 26K22,less pins. While is does cost $1 or 2 more than the 'perfect PIC for a project', I KNOW it WILL work. Also, instead of buying a PIC with builtin USB, I chose to buy external TTLUSB modules. yes, it costs me $1 more than a handful of parts BUT they work, NO code needed either.
So while it costs more for the parts, I save on R&D time, which saves money and gets the projects finished faster.

[rodrigo_cirilo]

Thanks for the previous answers.

I had a doubt, is it possible to use a mosfet as a 1bit memory?
I read somewhere that it keeps the last state, how would that work, or am I crazy?

[temtronic]

crazy...
Reality is that even though you only need 1 bit of memory .... 3 days from now, you'll need a whole byte , or 2 or 3 or 8........
projects NEVER,EVER get smaller..they expand to comsume ALL the resources of the PIC, and then some.
Last one I did, client 'needed' another 3 LEDS,sigh, that used up all but 1 pin of the 46k22 ! I came close to Charliplexing.....

[rodrigo_cirilo]

In this project I would really only need 1 bit to save the last state.
But ok, thanks for answering.

[jeremiah]

I believe they make non volatile latches you can buy, which would be one bit.

As far as the mosfet route, it won't do it on its own. You'll need some sort of capacitance to hold the state once power is cut. For that you need to determine how long the power will be off and pick a capacitance that will hold the charge some percentage longer than that for wiggle room.

[Ttelmah]

What is being wanted, could be done simply with a couple of CMOS gates.
As Jeremiah says, with a bit of added capacitance. Use low leakage capacitors
and a value could be held easily for weeks. No need for a PIC at all.

[temtronic]

or, just use 1 bit from the core memory of a PDP-5/8.
gee, ANYONE have any ? Mine got tossed few year back,by mistake.
I can't see any option truly cheaper in parts/labour/R&D time than a $2 RTC module or a different PIC.